Turbo machinery speed monitor

ABSTRACT

This invention relates to a speed monitor apparatus for monitoring speed and acceleration of rotating turbine equipment (turbomachinery) and for operating an overspeed trip to shut down the equipment in the event that the speed or acceleration exceed predetermined thresholds. The invention provides a speed monitor module having an input conditioner comprising: a multiplexer; an amplifier; and a comparator; in which the multiplexer selects an input signal from the sensor, or an input signal via a feedback loop from the comparator in dependence upon a test input, such that the input circuit may be tested by confirming that the amplifier oscillates when the feedback loop is enabled by the test signal.

BACKGROUND OF THE INVENTION

This invention relates to a speed monitor apparatus for monitoring speedand acceleration of rotating turbine equipment (turbomachinery) and foroperating an overspeed trip to shut down the equipment in the event thatthe speed or acceleration exceed predetermined thresholds.

Turbomachinery is used in many industries including oil and gasproduction and refining, chemical production and processing, powergeneration, paper and textile mills and sewage treatment plants.

It is desirable that turbines used in such industries have some form ofoverspeed protection system which will shut down the turbine in theevent that a fault condition causes the turbine to rotate too quickly orfor the speed of rotation to accelerate too quickly.

This invention provides improvements to known electronic overspeedprotection systems.

SUMMARY OF THE INVENTION

According to the invention there is provided a turbine speed monitormodule comprising: a sensor for generating a sensor signal in dependenceupon rotational speed of a turbine a module arranged to receive saidsensor signal and arranged in operation to generate a trip signal independence thereupon; wherein said sensor signal is converted to adigital signal by an input conditioner comprising: a multiplexer; anamplifier; and a comparator; in which the multiplexer selects an inputsignal from the sensor, or an input signal via a feedback loop from thecomparator in dependence upon a test input, such that the input circuitmay be tested by confirming that the amplifier oscillates when thefeedback loop is enabled by the test signal.

Preferably said module comprises a module slice and an output switch andthe module slice comprises said input conditioner; a trip controllerarranged to receive said digital signal and to generate an overspeed oroveracceleration signal therefrom; and an output controller arranged toreceive said overspeed or overacceleration signal and to generate saidoutput signal therefrom.

Preferably, said module comprises three identical module slices and saidtrip signal is generated by the output switch, the output switch beingarranged to receive an output signal from each one of the module slices,and in which the output switch comprises a two out of three voterarranged to receive a signal from each slice and generate a trip signaltherefrom.

In a preferred embodiment, said module is arranged to generate aplurality of trip signals and said output switch comprises a pluralityof two out of three voters each arranged to receive a signal from eachmodule slice and generate a trip signal therefrom.

In a preferred embodiment, each module slice comprises three inputconditioners connected to three trip controllers and the outputcontroller is arranged to receive an overspeed or an overaccelerationtrip signal from each one of said trip controllers, and in which saidoutput signal is generated according to a two out of three votingarrangement.

Still preferably there is a further output controller arranged toreceive an overspeed or an overacceleration trip signal from each tripcontroller, and arranged to generate a further output signal accordingto a two out of three voting arrangement.

In this case if the output controller is arranged to receive threeoverspeed trip signals and generate an overspeed trip signal then thefurther output controller is arranged to received three overaccelerationtrip signals and generate an overacceleration trip signal.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a block diagram of a speed monitor module;

FIG. 2 illustrates an input conditioner;

FIG. 3 illustrates a trip controller;

FIG. 4 illustrates an output controller;

FIG. 5 illustrates an output switch; and

FIG. 6 illustrates a trip output.

DETAILED DESCRIPTION

Referring now to FIG. 1 a speed monitor module 1 measures the speed andacceleration of up to three turbines. The invention will be described inrelation to one turbine only for reasons of simplicity. A fieldtermination assembly 2 provide an interface between sensors in the fieldand the module 1.

Input circuit 4 receives signals from sensors which may be activesensors, passive sensors or a combination of active and passive sensors.

The sensor inputs are arranged as a group of three inputs associatedwith a single turbine. The use of three sensors provides redundancy andfault tolerance.

Every sensor input is received by each one of three replicated moduleslices A B and C. Each slice A, B, C has three input conditioners 9.Each slice A, B, C has three trip controllers 6 each of which analyseseach of the input signals to determine the speed and accelerationmeasured by each sensor. Each sensor is analysed by each respective tripcontroller 6 to produce an ‘overspeed’ output trip signal and an‘overacceleration’ output trip signal when the speed or acceleration isdetermined to have risen to greater than a respective predeterminedthreshold. Two output controllers 7 generate two output signals independence upon either the three overspeed trip signals or the threeoveracceleration trip signals. Each output signal may be driven byanalysis of one, two or all three sensor inputs from the group asdetermined a trip controllers 6. The two output signals from each sliceare then used to produce four overspeed and overacceleration outputs foreach group of sensors by one of two output switches 10 using a two outof three voting system which is replicated four times. The fouroverspeed and overacceleration outputs for each group are then used todrive a pair of trip output modules 11 in one of three field terminationassemblies 2.

A host interface unit 5 interfaces to each one of the input conditioners9, to each one of the trip controllers 6 and to each one of the outputcontrollers 7 to provide configuration data, test and diagnosticsignals, and to receive diagnostic data. The HIU 5 provides informationto all three slices and also caters for signal routing between thevarious modules on each slice.

The Host Interface Unit provides software functionality for a slice. TheHIU is also triplicated to provide fault tolerance.

FIG. 2 illustrates the input conditioner 9. The input conditioner 9receives analogue sensor signals from the field termination assembly 2.The passive sensor provides a differential signal 24, which passes viafilter 26, through multiplexer 26 a and amplified by an amplifier 26 band then compared to a threshold by a comparator 27. The output is adata signal 28 comprising a digital pulse train of the same frequency asthe differential input signals 24. The output data signal 28 is isolatedby a galvanic isolator 29.

A test input 23 is provided from the host interface unit 5 via agalvanic isolator 25. The test signal can be used to causes multiplexer26 a to select as an input the output from the comparator 27 via afeedback connection 29. This causes the amplifier 26 b to oscillate andprovides a method of testing the input circuitry 9.

FIG. 3 illustrates a trip controller 6 on a slice A, B or C. The tripcontroller 6 receives configuration data 36 from the host interface unit5. The configuration data comprises:

Number of gear teeth, from 1 to 1000.

Over speed trip mode, latching or non-latching

Over acceleration trip mode, latching or non-latching.

Overspeed trip sense.

Overacceleration trip sense.

Overspeed trip threshold in RPM.

Overspeed test trip threshold in RPM.

Overspeed test timeout.

Overacceleration trip threshold in RPM/M.

Overspeed trip dead-band.

Overacceleration trip dead-band.

The overspeed trip sense and overacceleration trip sense are binaryvalues which determine which are used by diagnostics to determinewhether there is a current through trip relay in the trip output modulein response to detection of an overspeed or overacceleration condition.The overspeed and overacceleration dead-bands define when a detectedoverspeed or overacceleration will revert to a non-tripped condition.The deadbands may be defined as a percentage of the trip thresholds oras an absolute value, and provide hysteresis in the system. However,when a latching mode is selected the trip remains once an overspeed oroveracceleration trip is detected even if the condition is transient.

Data signal 28 is received from input signal conditioner 9. The tripcontroller uses the data signal 28 and the number of gear teeth tocalculate the turbine speed in revolutions per minute (RPM) in thisembodiment of the invention the speed is determined to within 0.5 RPM todetermine a speed output signal 31. The acceleration is also calculatedin RPM per minute (RPM/M) to determine an acceleration output signal 32.The maximum speed reached is also determined, by comparing the presentspeed to a stored maximum speed and replacing the stored maximum speedwith the present speed if the stored maximum speed has been exceeded. Asignal 33 representing the maximum speed reached is also provided to theHIU where they may be used by other control functions or displayed tothe user.

There are two overspeed thresholds; the overspeed trip threshold and theoverspeed test trip threshold. A binary test input 37 determines whichtrip threshold is selected to determine the state of a binary overspeedtrip output 34.

The determined speed is compared to the selected trip threshold. If thespeed exceeds the selected trip threshold, then the overspeed tripoutput 34 will be set or cleared depending on the overspeed trip senseconfigured by the host interface unit 5.

In general the overspeed trip threshold is used. However there arecircumstances where it is desirable to allow the turbine to exceed thisthreshold without causing the speed monitor module to detect anoverspeed condition and shut down the turbine. As well as having anelectronic overspeed protection system a turbine may also have amechanical overspeed protection system which will shut down the turbineat a higher speed than the electronic overspeed protection system. Inorder to test the mechanical overspeed protection system it is necessaryto use a higher trip threshold in the electronic speed protection systemso that the mechanical protection system is allowed to operate.

In the event that the speed rises to greater than the overspeed testtrip the overspeed trip output is set. In the event that the timeallowed by the overspeed test timeout expires the threshold is reset tobe equal to the original overspeed trip threshold.

The determined acceleration is compared to the overacceleration tripthreshold. If the determined acceleration exceeds the overaccelerationtrip threshold, then an overacceleration trip output 35 is set.

The test and diagnostic signals are provided from and to the HIU 5. Inthe event that any errors are detected the trip controller 6 can be putinto a fail safe condition or alternatively and alarm can be raised.

The speed monitor module may be plugged in to the same chassis as amodule which is controlling the speed of the turbine. However, it isimportant that the speed controller cannot interfere with the speedmonitor in anyway because most overspeed conditions are caused by afault in the speed controller and it is important that a fault in thespeed controller does not cause the speed monitor to fail.

In order that the trip threshold can not be altered by a main processorwhich controls both the speed controller and the speed monitor, duringuse the configuration data may only be loaded when the turbine speed isless than a particular threshold (usually stopped). Furthermore when theoverspeed test trip threshold is used it is controlled by a timeout sothat the monitor module does not remain in this condition.

These features allow the speed monitor module to operate independentlyof the turbine speed control system so that in the event that theturbine speed control system fails it cannot alter any parameters usedby the speed monitor module and the speed monitor module can still shutthe turbine down reliably.

FIG. 4 illustrates an output controller 7 on a slice A, B or C.

The output controller 7 receives three signals from three tripcontrollers via the HIU 5. Either three overspeed trip outputs 34, 34′,34″ or three overacceleration trip outputs 35, 35′, 35″ are received.The three trip outputs are arranged to relate to the analysed data fromthree sensors from a group. Configuration data received from the hostinterface unit determines which trip outputs are received by the outputcontroller 7, and which of the three received trip outputs are used togenerate a switch control output 41.

Diagnostic data 43 may be received from the output switch 10 anddiagnostic data may be provided to the HIU 5, relating to the status ofthe output controller 7 and to the output switch 10.

Test input and override signals 45, are provided by the HIU 5 forallowing testing of the output controller 7. In particular a trip may beforced.

FIG. 5 illustrates an output switch 10 which is used to drive the tripoutput module 11 on the field termination assembly 2.

Each output switch 10 accepts three inputs 41A, 41B, 41C (correspondingto a signal from each slice A, B and C from corresponding outputcontrollers 7, the signal being a switch control signal 41 relating tooverspeed or overacceleration from a particular group of sensors). Thevoting circuitry in the output switch 10 is replicated four times asfour separate circuits to provide four outputs which are used to driverelays in the trip output module 11.

The output switch 10 has diagnostic output signals 43A, 43B, 43C whichare connected to the diagnostic input port on said corresponding outputcontrollers 7.

The diagnostic information includes relay drive status, relay contactstatus and current in each leg of the output relay structure of the tripoutput module 11. The diagnostic information relating to relay contactstatus and current in each leg of the output relay structure is receivedvia diagnostic input signals 101, 102, 103 from the trip output module11 and sent via monitors 55, 56, 57 to the relevant output controllerson each slice A, B, C.

The output switch 10 has four ‘two out of three’ voters 52 a, 52 b, 52c, 52 d which are connected to all three inputs 41A, 41B, 41C. Theresult of the two out of three vote is made available via relay drivers53 a, 53 b, 53 c, 53 d, as corresponding signals 58 a, 58 b, 58 c, 58dto the trip output module 11.

The signals 58 a, 58 b, 58 c, 58 d are also sent via a relay drivestatus block 54 to the relevant output controllers 7 on each slice A, B,C for diagnostic purposes.

Each field termination assembly 2 may be considered to comprise an inputfield termination assembly and an output field termination assembly. Theinput field termination assembly comprises three input circuits 4.

These inputs 4 contain surge suppression and filtering componentsnecessary to protect module circuits against high voltage transients andfaults. Pulses that arrive from the sensors can vary in amplitude fromseveral hundred millivolts to over 100 volts. A termination resistor inthe input circuit 4 reduces the amplitude to a maximum of about 10volts.

The field termination assembly 2 may also serve as a distribution pointfor supplying power to any active sensors in the field.

The output field termination assembly comprises two trip output circuits11.

FIG. 6 illustrates a trip output circuit 11. The overspeed trip circuitand the over acceleration circuit are identical to one another and areimplemented on by single trip output circuit. For simplicity only asingle trip circuit is illustrated.

Clamped armature relays are labelled as follows: a reference numeral61,62,63,64 indicates a relay driver and reference numerals 61 a,61 betc indicate a pair of clamped armatures. One of he clamped armaturese.g. 61 a is energised or de-energised and the other e.g. 61 b movessimultaneously. This means that if one of the pair of clamped aramatures61 a, 61 b becomes stuck in one position the armature of the relay towhich it is clamped will ‘float’ between contacts, allowing a fault tobe detected.

Referring still to FIG. 6, a trip output circuit is arranged so that asingle relay failure or faulty input will not cause a failure.

The relays are arranged such that they are normally energised and arede-energised to trip. Signals 58 a, 58 b, 58 c, 58 d are used to driveeach armature clamped relay 61, 62, 63, 64. A first armature of eachpair 61 a, 62 a, 63 a, 64 a forms two parallel electrical paths whichare connected via a load 65 when the relays 61, 62, 63, 64 areenergised. In the event of an overspeed condition, if any one of therelay contacts fails to open there will still be an electrical breakallowing the overspeed trip to function. Two Hall effect sensors 66 a,66 b detect whether there is current flowing in both parallel paths andif only one is active then this is detected via feedback signals 68 a,68 b.

Such an error could be caused either by a failure of one of the relays61 a, 62 a, 63 a, 64 a, or by an error in one of the input signals 58 a,58 b, 58 c, 58 d.

In order to determine the likely cause, the second armature of each pair61 b, 62 b, 63 b, 64 b are connected to form an electrical path which iscontinuous as long as each one of the armatures 61 b, 62 b, 63 b, 64 bis in an open or a closed configuration. Only in the event that anarmature 61 b, 62 b, 63 b, 64 b is floating between an open and a closedposition will the electrical path be discontinuous. This will happenwhen one of the armatures 61 a, 62 a, 63 a, 64 a, has become stuck.Therefore feedback signal 69 may be used, in conjunction with signals 68a and 68 b to determine whether a fault is due to a fault in the outputrelays or due to a faulty input signal. The signals 68 a and 68 b areused to check than there is current in both paths when a fault isdetected.

A single signal 69 may be used to indicate a ‘stuck’ fault on any numberof clamped armature pair relays, and may be used to indicate a faultrelating to a fault in either an overspeed trip output circuit or anoveracceleration trip output circuit.

It will be appreciated that various alterations, modifications, and/oradditions may be introduced into the constructions and arrangements ofparts described above without departing from the scope of the presentinvention as defined in the following claims.

1. A turbine speed monitor module comprising: a sensor for generating asensor signal in dependence upon rotational speed of a turbine a modulearranged to receive said sensor signal and arranged in operation togenerate a trip signal in dependence thereupon; wherein said sensorsignal is converted to a digital signal by an input conditionercomprising: a multiplexer; an amplifier; and a comparator; in which themultiplexer selects an input signal from the sensor, or an input signalvia a feedback loop from the comparator in dependence upon a test input,such that the input circuit may be tested by confirming that theamplifier oscillates when the feedback loop is enabled by the testsignal.
 2. A turbine speed monitor module according to claim 1 in whichsaid module comprises a module slice and an output switch and the moduleslice comprises said input conditioner; a trip controller arranged toreceive said digital signal and to generate an overspeed oroveracceleration signal therefrom; and an output controller arranged toreceive said overspeed or overacceleration signal and to generate saidoutput signal therefrom.
 3. A turbine speed monitor module according toclaim 2, in which said module comprises three identical module slicesand said trip signal is generated by the output switch, the outputswitch being arranged to receive an output signal from each one of themodule slices, and in which the output switch comprises a two out ofthree voter arranged to receive a signal from each slice and generate atrip signal therefrom.
 4. A turbine speed monitor module according toclaim 3, in which said module is arranged to generate a plurality oftrip signals and said output switch comprises a plurality of two out ofthree voters each arranged to receive a signal from each module sliceand generate a trip signal therefrom.
 5. A turbine monitor moduleaccording to claim 4, wherein each module slice comprises three inputconditioners connected to three trip controllers and the outputcontroller is arranged to receive an overspeed or an overaccelerationtrip signal from each one of said trip controllers, and in which saidoutput signal is generated according to a two out of three votingarrangement.
 6. A turbine monitor module according to claim 5, furthercomprising a further output controller arranged to receive an overspeedor an overacceleration trip signal from each trip controller, andarranged to generate a further output signal according to a two out ofthree voting arrangement.